Electromagnetic reed relay having low noise characteristics



lan. 28, 1969 N. H. MAGIDA ETAL 3,425,008

ELECTROMAGNETIC REED RELAY HAVING LQW NOISE CHARACTERISTICS -F.iled Dec. 8, 1966 Sheet I of s k i i M J I INVENTORS'.

( )Vaiizan H. Mag 422a flleninder Z. Lopasw 19 B Wi lliam [Jo/filer Flair Buckles X Lesari JITTORNWS.

n- 1959 N. H. MAGIDA ETAL 3, 5,008

ELECTROMAGNETIC REED RELAY HAVING LOW NOISE CHARACTERISTICS Filed Dec. 8, 1966 Sheet 2 of 3 Jan. v28, 1969 N. H. MAGIDA ETAL 3,425,003

ELECTROMAGNETIC REED RELAY HAVING LOW NOISE CHARACTERISTICS Sheet 9 of Filed Dec. 8, 196

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, VII/l [rill/4 United States Patent 3,425,008 ELECTROMAGNETIC REED RELAY HAVING LOW NOISE CHARACTERISTICS Nathan H. Magida, Westport, and Alexander Z. Lopasic,

Stamford, Conn., and William Wolfner, Columbus, Ind., assignors to Thermosen, Incorporated, Stamford, Conn.

Filed Dec. 8, 1966, Ser. No. 600,188 US. Cl. 335--93 Int. Cl. H01h 51/34 13 Claims ABSTRACT OF THE DISCLOSURE Background and objects of the invention Reed relays are frequently used in low level switching applications, and as a consequence, the problem of spurious signal noise introduced into the circuits being switched by and through the relay itself becomes significant. Switching noise falls into two general categories. The first includes spurious signals introduced into the switched circuits through the relay contacts from external sources by inductive or capacitive coupling. Generally, this can be minimized through the use of conventional shielding techniques. The second category of switching noise includes static and dynamic noise originating in the relay itself.

The most significant source of static noise is thermally generated voltages resulting from temperature differentials across bi-metallic junctions in the electrical contact elements of the relay and at the connections between these contact elements and the external circuit. Dynamic noise in reed relays arises principally from generator and magnetostrictive effects because the movable contact reeds are positioned in the magnetic field created by the relay operating coil or, in fact, constitute a part of the relay magnetic circuit.

It will be appreciated that if movement of the electrically conductive reed results in magnetic lines of force being cut, spurious voltages are induced therein. This is the so-called generator effect. If the reeds are included in the magnetic circuit, the flux reacts with stresses produced in the reed by virtue of its movement to create magnetostrictive effects. Spurious voltages are thereby generated which may become quite significant where the signal voltages of the circuits being switched are in the high micro-volt range.

Still another shortcoming of many prior art electromagnetic reed relays is that the relay contact gaps are also disposed in the magnetic field created by the operating coil. After a period of use, microscopic particles are eroded from the contact surfaces and also from the reeds themselves. Those particles may become magnetized due to the presence of the magnetic field or may already be magnetic in nature. Since flux is concentrated at the gaps between the switch contacts, these magnetic particles will accumulate there. Such accumulations alter the magnetic characteristics of the relay as well as the contact resistance. Ultimately, bridging of the switch contacts may occur.

Accordingly, it is an object of the present invention to provide an improved electromagnetic relay.

A more specific object of the present invention is to pro- Patented Jan. 28, 1969 ice vide an electromagnetic reed relay having extremely low noise characteristics as compared to prior reed relays.

An additional object is to provide a reed relay of the above character wherein the potential to produce static noise signals is substantially reduced.

A further object is to provide a reed relay of the above character wherein the potential to produce dynamic noise signals is substantially reduced.

Still another object is to provide a reed relay of the above character which is of miniature physical size and thus conductive to high density packaging.

An additional object is to provide a reed relay of the above character capable of high speed operation; and having long operating life, low and stable contact resistance, and relatively high contact ratings.

Still another object is to provide a reed relay of the above character which is simple in design and inexpensive to manufacture.

Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises an article of manufacture possessing the features, properties and the relation of elements which will be exemplified in the article hereinafter described, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIGURE 1 is a perspective view of a relay embodying the invention;

FIGURE 2 is a perspective view of the various parts of the relay of FIGURE 1 shown in disassembly;

FIGURE 3 is a side elevation sectional view taken along line 33 of FIGURE 1;

FIGURE 4 is a side elevation sectional view taken along line 4-4 of FIGURE 1;

FIGURE 5 is a cross sectional view taken along line 55 of FIGURE 3;

FIGURE 6 is a cross sectional View taken along line 6-6 of FIGURE 3;

FIGURE 7 is a cross sectional view taken along line 7-7 of FIGURE 3; and

FIGURE 8 is a cross sectional view taken along line 8-8 of FIGURE 3.

Similar reference characters refer to like parts throughout the several views of the drawings.

General description- In the disclosed relay construction, the movable contact .reed is so positioned relative to the relay magnetic circuit to be substantially beyond the magnetic field developed by the operating coil and, at the same time, to drastically reduce the relay size. The reed forms no part of the magnetic circuit and, in fact, is shielded by a fluxcarrying member of the magnetic circuit. As a consequence, generator and magnetostrictive effects are substantially reduced with resultant reductions in dynamic noise. Since the reed does not constitute a part of the magnetic circuit, it may be fabricated from high conductivity metals to provide low contact resistance rather than conductive magnetic alloys which required the reed to carry one or more separate high conductivity contact button or have precious metal plated surfaces. Consequently, bimetallic junctions in the relay electrical circuit elements are avoided and thermally generated voltages are substantially reduced. The contact gap is also located substantially beyond the relay magnetic field and therefore the tendency to accumulate particles thereat is essentially avoided.

Detailed description Referring specifically to the drawings, the present invention is embodied in a reed relay, generally indicated at 10 in FIGURE 1. The relay 10, includes a housing 12 constructed of a suitably rigid plastic, such as diallyl phthalate. The housing 12, is closed by a three-sided, snap-on cover member, 14. A variety of terminal pins, commonly indicated at 16 in FIGURE 1, project through the bottom of the housing 12 for insertion in a plug receptacle such as may be incorporated in a printed circuit board. The reed relay 10 may be of miniature size having dimensions, exclusive of terminal pins 16, on the order of three-eights by three-eighths by thirteen-sixteenths of an inch, and consequently, is ideally suited for miniaturized printed circuit applications.

Referring now to FIGURE 2, the housing is formed with integral sidewalls 18 and 19, a front wall 20, and a floor 22. A saddle 24 and an elongated land 26, extending from a point adjacent the saddle to the front wall 20 of the housing 12, support an elongated shell 28, formed from a suitable magnetic alloy of high permeability. The shell 28 has a substantially arcuate cross-sectional configuration with flaring lateral edge portions 28 resting on elongated ledges 30 integrally formed with the housing sidewalls 18 and 19. The mounting of the shell 28 within the housing 12 is best seen in FIGURES 4 through 7.

A coil assembly, generally indicated at 32, consists of a plurality of turns of conductive wire wound about a bobbin 34. The coil assembly 32, rests on the elongated shell 28 as is seen in FIGURES 3, 4, 7 and 8. The bobbin 34 has a central bore 35 for receiving an elongated core 36 formed of a suitable magnetic alloy of high permeability. The core 36 has an enlarged annular end portion 38 serving as a magnetic pole piece. A rigid plastic header 39, interposed between the pole piece 38 and the core assembly 32 and receiving the core 36 in a central hole 40, is provided with laterally extending ears 41 received in vertically extending grooves 42 formed in housing sidewalls 18 and 19 (FIGURE 6). A Washer 44 is force fitted on the end of the core 36 extending beyond the coil assembly 32 as is seen in FIGURE 4. With the various parts thus described positioned within the housing 12, the washer 44, formed of a suitable magnetic alloy, is in physical contact with the right-hand end portion of the shell 28 as is seen in FIGURE 4.

The relay coil is energized through a pair of coil lead pins 48 (FIGURES 2 and 8) which extend through apertures 49 in the housing floor 22 and upwardly in vertical grooves 50 formed in the housing sidewalls 18 and 19 to terminations located generally above the coil assembly 32 for convenient electrical connection to the free ends of the relay coil winding. A grounding pin 52 projects through a hole 53 in the housing floor 22 and extends upwardly in a recess 54 formed in the saddle 24 (FIGURES 2, 4 and 7). The grounding pin 52 terminates in electrical contacting engagment with the shell 28 and thus serves to ground the magnetic circuit of the relay 10. In addition, the grounding pin 52 may also serve as a keying pin effective to prevent improper insertion of the relay in a plug receptacle.

Referring jointly to FIGURES 2 and 3, a pair of vertical reed terminal pins 56 are introduced into the housing 12 through holes 57 formed in the floor 22. The upper ends of the terminal pins 56 carry cantilevered reeds 60 extending horizontally beneath the shell 28 in channels 62. The reeds 60 are preferably formed as integral extensions of the reed terminal pins 56 by flattening the round stock of the terminal pins to provide necessary flexibility. As is best seen in FIGURES and 6, the reeds 60 are formed such that they lie in a plane which is approximately 30" from horizontal in order to avoid interference with the shell 28 upon deflection of the reeds.

Again referring to FIGURE 3, terminal pins 64 project into the interior of housing 12 through holes 65 in the housing floor 22. The upper end portions of the terminal pins 64 are bent at right angles to extend horizontally for a short distance in underlying relationship to the reeds 60. The ends of these horizontal extensions are formed into fixed break contacts 66 normally in electrical contacting engagement with the reeds.

Terminal pins 70 are introduced into the interior of housing 20 through holes 71 formed in the housing floor 22. The upper ends of terminal pins 70 are formed having a hooked configuration such that they extend around the free ends of the reeds 60 to present fixed make contacts 72 overlying the free end portions of the reeds.

In order to transfer the reeds 60 from normal electrical contacting engagement with the fixed break contacts 66 to electrical contacting engagement with the fixed make contacts 72, a U-shaped reed plate member, generally indicated at 76, is afiixed at its leg 77 to the upper of each reed 60. The base portion 78 of each reed plate 76 extends radially inwardly, skirting the left-hand end of shell 28 as seen in FIGURE 3, and carries an integrally formed leg 79' extending horizontally into a gap 46 between pole piece 38 and the marginal inner surface of the shell 28 adjacent its left end. The reed plate 76 is formed of a suitable magnetic alloy of high permeability.

Referring to FIGURE 4, the magnetic circuit for the relay 10 effectively includes pole piece 38, core 36, end plate 44, shell 28, gap 46 and the legs 79 of reed plates 76 disposed in gap 46. Due to the relative dimensions of the peripheral surface of pole piece 38, the reed plate legs 79, and the inner marginal surface portion of shell 28 adjacent its left end, it is seen in FIGURE 5 that gaps 46' between these reed plate legs and the pole piece are of smaller area than gaps 46" between the reed plate legs and the shell. As a consequence, when the coil is energized and flux flows across gaps 46', 46" and through reed plate legs 79, the reed plates 76 are attracted toward the pole piece 38. This results in the transfer of the reeds 60 from electrical contact with the fixed break contacts 66 to electrical contact with the fixed make contacts 72. This is because the force between two poles separated by a non-magnetic gap is inversely proportional to the crosssectional area of the gap. Since gaps 46' are of smaller area than gaps 46", positive forces are created to move the reed plates 76 toward the pole piece 38. Movement of the reeds is arrested upon engagement with the fixed make contacts 72, and thus the reed plates 76 cannot contact the pole piece 38. Similarly on release, the reeds engage the fixed break contacts 66 before the reed plate can contact the shell 28.

A cover member 82 (FIGURE 2) is positioned in the housing 12 with its rearward edge portion resting on the top edge of header 39 and its front edge portion supported on a ledge 83 integrally formed with the housing front wall 20 (FIGURES 3 and 4). The lateral edge portions of the cover member 82 are flared outwardly to rest on ledges 84 integrally formed with the housing sidewalls 18 and 19 (FIGURES 2 and 5). An epoxy (not shown) is poured over the cover member 82 and header 39, and along the edges of shell 28 to secure and seal them in position. In addition, an epoxy 85 is poured over the bottom surface of the housing floor 22 to hermetically seal off the various points of entry into the housing 12 for the terminal pins. Thus there is created a hermetically sealed compartment which includes the previously designated reed channels 62 and a second chamber, designated 88, in which the reed plates 79 and the fixed make contacts 72 are positioned. As seen in FIGURES 3, 7 and 8, a metal tube is introduced longitudinally through the saddle 24 adjacent the housing floor 22 for the purpose of evacuating the channels 62 and contact chamber 88. Once this is accomplished, the outer end of the tube 90 is pinched off leaving a non-corrosive atmosphere in which the various relay contacts may operate. In addition, while the relay 10 is in use, corrosive gases, dirt, and other contaminants are precluded from entering into the contact chamber 88 and reed channels 62. If desired, this compartment, once evacuated, may be backfilled with a suitable inert gas through the tube 90- before its exterior end is pinched 01?.

Summary From the foregoing detailed description, it is readily seen that the present invention provides a reed relay having extremely low noise characteristics. Measurements indicate that dynamically-generated noise is approximately three microvolts, peak to peak; a substantial reduction over prior art reed relays. It is appreciated that it is virtually impossible to completely eliminate dynamic noise under conditions where, as here, the contact reeds 60 are positioned in close proximity to the relay coil. While the shield 28 substantially shields the reed 60, there is some unavoidable fringe magnetic field enveloping the reeds.

With the reeds 60 and the fixed contacts 66 and 72 formed of a similar metal such as a gold-diffused, silver magnesium nickel alloy, thermally-generated voltages resulting from the heat developed by the relay coil have been measured at less than four microvolts. The source or sources of the thermally-generated voltages have not been isolated, but it is suspected that it originates in large part from the contact junction between the terminal pins 16 and the external circuit. Nevertheless, this noise figure is substantially less than that encountered in prior art reed relays. By virtue of these extremely low noise figures, the disclosed relay is ideally suited for use in precision analog switching systems, including high-speed scanners.

Operate and release times, including bounce, have been measured at 1.5 milliseconds maximum. Consequently, the disclosed relay is particularly useful in computer and communication switching logic systems and other such applications where speed rather than low noise is the prime consideration. Due to the ability of using relatively large masses of excellent contact materials in the formation of reeds 60, increased contact switching reliability and capability are achieved.

It will be appreciated that by positioning the reeds 60 such as to be substantially co-extensive with the coil assembly 32, the length of the relay is significantly reduced. In fact, the overall length of the relay is largely determined by the length dimension of the coil assembly plus pole piece. This should be contrasted with the relay construction shown in Magida et al., U.S. Patent No. 3,274,524 wherein the overall length is essentially determined by the length of the coil assembly and pole piece plus the length of the reeds.

While two sets of reeds and fixed contacts have been disclosed, it will be appreciated that a greater or lesser number of sets may be employed without departing from the invention.

It will thus be seen that the objects set forth above, among those made apparent from the preceding descrip tion, are efiiciently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described our invention, what we claim as new and desire to secure by Letters Patent is:

1. An electromagnetic reed relay comprising, in combination;

(A) a magnetic circuit having a gap therein, said circuit including A (1) a core, (2) a coil surrounding said core,

(3) a pole piece afiixed to one end of said core,

(4) an end plate aifixed to the other end of said core, and

(5) a shell extending in substantially parallel spaced relationship to said core,

(a) said end plate contacting one end of said shell,

(b) said gap located between said pole piece and a surface portion of said shell adjacent its other end.

(B) at least one flexible, electrically conductive reed disposed on the opposite side of said shell from said core in parallel, spaced relationship to said shell, said reed having (1) a major portion of its length co-extensive with a portion of the length of said shell between said ends thereof, and

(2) an extension extending around said other end of said shell and into said gap,

(a) said extension being acted upon by said magnetic circuit to move said reed; and

(C) at least one fixed contact,

(1) said reed movable to and from electrical contacting engagement with said fixed contact.

2. An electromagnetic relay comprising in combination: a magnetic core, an electrically conductive coil surrounding said core, a magnetic pole piece affixed to one end portion of said core, a magnetically permeable shell extending in substantially parallel spaced relationship to said core, a magnetically permeable end plate engaging the other end portion of said core and one end portion of said shell; said core, pole piece, shell and end plate forming a magnetic circuit having a gap located between the other end portion of said shell and said pole piece; at least one fixed electrical contact, at least one resilient electrically conductive reed capable of moving to and from electrically contacting engagement with said fixed contact; and a magnetically permeable member aflixed to said reed, said member extending away from said reed and having a segment thereof positioned in said gap to become a part of said magnetic circuit, whereby the flow of flux across said gap and through said segment develops forces exerted on said segment effective to move said reed.

3. The relay defined in claim 2 wherein said reed is formed of a non-magnetic, high conductivity metal.

4. The relay defined in claim 3 wherein said reed provides a unitary metallic, electrically conductive circuit path between an input terminal connected thereto and said fixed contact.

5. The relay defined in claim 4 wherein said fixed contact is formed of the same material as said reed.

6. The relay defined in claim 2 wherein (1) said segment divides said gap into a first gap portion between it and said pole piece and a second gap portion between it and said shell,

(2) said first gap portion being of smaller area than said second gap portion.

7. The relay defined in claim 2 wherein 1) said shell is located between said reed and said core with said reed extending in parallel spaced relationship thereto,

(2) said shell having a dimensional configuration effective to magnetically shield said reed.

8. The relay defined in claim 7 wherein (1) said shell has a substantially arcuate cross-sectional configuration.

9. The relay defined in claim 2 which further includes (A) a housing having (1) a pair of sidewalls and a floor,

(2) ledges carried by said sidewalls and supports extending upward from said floor for supporting said shell in spaced relation to said floor,

(a) said reed positioned in the space between said shell and said floor, and

7 (3) the assembly of said core, coil and end plate being supported on said shell,

(B) a header interposed between said coil and said pole piece, said header having (1) a hole receiving said core, and (2) lateral extensions received in grooves formed in said sidewalls.

10. The relay defined in claim 9 which includes (1) a fixed break contact underlying said reed and normally in electrical contacting engagement therewith,

(2) said reed being cantilever mounted,

(3) a fixed make contact overlying the free end portion of said reed in normally spaced relationship thereto.

11. The relay defined in claim 10 which includes (1) plural reeds, and

(2) fixed break and fixed make contacts operatively associated with each reed.

12. The relay defined in claim 9 wherein said housing References Cited UNITED STATES PATENTS 9/1959 Umrath 335-93 12/1959 Buccini 335-98 11/1962 Bosch 335--93 3 /1965 Williams 335-81 2/1967 Highley 33597 OTHER REFERENCES Komolibus, E.: D.C./A.C. Converters for DC. Am-

plifiers. British Scientific Instrument Research Association. 1961, page 6.

BERNARD A. GILHEANY, Primary Examiner. HAROLD BROOME, Assistant Examiner. 

